The research described in this AREA application is responsive to recommendations in the Report of the Prostate Cancer Progress Review Group (PRG). Recent data demonstrate that high selenium (Se) intake or status and high intake of phytoestrogens (isoflavones) each provide a protective effect against prostate cancer, and that their combined use may provide greater benefit than either dietary component alone. The PRG report recommends "Support studies aimed at better understanding of the roles in androgen production and in prostate physiology of nutrients such as ... selenium [and] phytoestrogens..." The objective of this work is to assess the cancer protective effects in prostate of high consumption of Se and isoflavones, individually and in combination, and to assess the critical effect of the timing of dietary exposure. Recent results from animal studies suggest that exposure begun at conception produces beneficial effects not seen when exposure is started after sexual maturation. To identify biochemical and molecular mechanisms for those effects, attention will focus on processes regulated by the androgen receptor (AR) and by NF-:B. Specific Aim 1 is to demonstrate that high dietary intake of Se and isoflavones, individually and in combination, will inhibit progression of prostate cancer in TRAMP (TRansgenic Adenocarcinoma of Mouse Prostate) mice, dependent on the timing of dietary intervention. Beginning at different time points (conception, 6, 12, and 18 weeks) and continuing to different end points (6, 12, 18 and 24 weeks), TRAMP mice will be fed diets adequate or high in Se, and low or high in isoflavones in a 2 X 2 factorial design. Measurement of body weight, genitourinary (GU) tract weight, time to palpable tumor, pathological tumor grade, and incidence of metastases will be determined for all animals sacrificed at each time point. Specific Aim 2 is to demonstrate that high dietary intake of Se and isoflavones, individually and in combination, will reduce activation of the androgen receptor (AR) and NF-:B, and decrease expression of AR- and NF-:B-regulated genes in prostates of TRAMP mice, dependent on the timing of dietary intervention. Blood levels of androgen, IGF-1, and GH will be measured by ELISAs, total Se by fluorometry, and isoflavone levels by HPLC. Se-dependent glutathione peroxidase and 5alpha-reductase activities will be assayed. AR and NF-:B activation will be determined by EMSA. Expression of AR- and NF-:B-regulated genes relevant in prostate cancer, whose expression is also modified by Se and/or isoflavones, will be examined by RT-PCR. These assays will show individual effects for each dietary component, the modifying effects each has on the other's metabolism, and the effects of combined use on the end points of interest. Correlation of these measures with time of dietary intervention and disease progression will identify the period(s) during tumor growth when supplementation may be most efficacious. This work will identify mechanisms of chemoprevention by combined consumption of different protective dietary components and the optimum time during tumorigenesis for dietary intervention. PUBLIC HEALTH RELEVANCE: This work will accomplish several objectives outlined by the Prostate Cancer Progress Review Group and by the NIH Five Year Plan "Planning for Prostate Cancer". These include 1) "defining the role of specific dietary factors in the etiology and prevention of...cancer";2) increasing "understanding of the roles in...prostate physiology of nutrients";3) definition of "the mechanisms by which these nutrients alter risk";and 4) demonstration of "the effects of nutrients on molecular events in the prostate". According to the NIH report "the effect of food constituents on molecular events in the prostate is unknown". Discovery of Se- and isoflavone-regulated genes will "identify biomarkers of the consumption of key dietary components".